The present invention relates to an aerogel substrate comprising an aerogel layer and a functional layer formed on a surface of the aerogel layer and a process for the production of the substrate.
An aerogel, particularly a silica aerogel has characteristic properties such as a heat insulating property, an electrically insulating property, a low refractive index and a low dielectric constant. Studies have been made to apply the aerogel to various fields using its properties. For example, a highly functional substrate can be manufactured by forming a thin film of a silica aerogel on a surface of a plate member such as a glass plate and so on and further forming a functional thin film on a surface of the silica aerogel thin film. For example, in the case where an electrically conductive metal (such as copper) thin film is formed as the functional thin film on the surface of the silica aerogel thin film and a circuit is formed with the electrically conductive metal thin film, a circuit board can be obtained in which the low dielectric constant of the silica aerogel is utilized.
The silica aerogel is prepared by hydrolyzing an alkoxysilane (which is referred to also as a silicon alkoxide or an alkyl silicate) followed by polycondensation of the alkoxysilane to obtain a gel compound, and drying the gel compound in the presence of a dispersion medium under supercritical conditions exceeding a critical point of the solvent, as disclosed in U.S. Pat. Nos. 4,402,927, 4,432,956 and 4,610,863. Further, as disclosed in Japanese Patent Kokai Publications Nos. 5-279011 and 7-138375, a hydrophobing treatment (a treatment for making a silica aerogel hydrophobic) improves moisture resistance of the silica aerogel and prevents deterioration of characteristic properties of the silica aerogel.
In order to produce a highly functional substrate using an aerogel such as a silica aerogel, it is required that a functional thin film is formed uniformly on a surface of the aerogel. However, it is difficult to form the thin film uniformly on the surface of the aerogel since the aerogel is a porous material. For this reason, a highly functional substrate in which an aerogel is used has not currently been put to its practical use.
The present invention has been accomplished in the light of the circumstances as described above, of which object is to provide an aerogel substrate which comprises an aerogel layer and a functional layer formed uniformly on a surface of the aerogel layer, and a process for producing the aerogel substrate.
In the first aspect, the present invention provides an aerogel substrate which comprises an aerogel layer, an intermediate layer which is formed on at least one surface of the aerogel layer and a functional layer which is formed on a surface of the intermediate layer, the functional layer being formed on the surface of the intermediate layer without penetration of a material constituting the functional layer into the aerogel layer.
xe2x80x9cWithout penetration of a material constituting the functional layer into the aerogel layerxe2x80x9d means that penetration of the material(s) which constitutes the functional layer into the aerogel layer through pores in the aerogel layer does not occur during and after formation of the functional layer. Such functional layer constitutes the aerogel substrate as a uniform layer (e.g. a thin uniform film) of which surface is continuous with a small surface roughness and performs a predetermined function well.
The aerogel substrate of the present invention is obtained by making the intermediate layer as a layer which prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer. xe2x80x9cPreventing the material(s) which constitutes the functional layer from penetrating into the aerogel layerxe2x80x9d means preventing the material(s) which forms the functional layer from penetrating into the aerogel through the pores in the aerogel layer during and after the formation of the functional layer. In the case where the formation of the functional layer involves a material which does not remain in the functional layer ultimately (for example, a solvent which evaporates by drying), the intermediate layer prevents also the penetration of such material. Therefore, the functional layer which is formed on the surface of the intermediate layer is a uniform layer (e.g. a thin uniform film) of which surface is continuous with a small surface roughness.
It is not necessarily needed that the intermediate layer completely prevents the penetration of the material(s) which constitutes the functional layer into the aerogel layer. As long as the functional layer is formed so uniformly that it can perform a desired function depending on its use or the like, it is acceptable that only a small amount of the material(s) constituting the functional layer penetrates into the aerogel layer. For example, in the case where the intermediate layer is not continuous in a part thereof and micropores (such as pinholes) are formed in the intermediate layer, even if the material(s) constituting the functional layer penetrates into the aerogel layer through the micropores, such penetration is accepted as long as the functional layer is formed uniformly as a whole and performs the desired function.
Alternatively, the aerogel substrate according to the present invention may be constructed by combining a specific intermediate layer with a specific aerogel layer and further selecting a specific material(s) which constitutes the functional layer (such as specific material(s) including a material (such as a solvent to be evaporated by drying) which is used only in the step of forming the functional layer), so that the material(s) constituting the functional layer may penetrate into the intermediate layer, but cannot penetrate into the aerogel layer from the intermediate layer. Such aerogel substrate is realized, for example, by making properties of the intermediate layer different from those of the aerogel layer so that the material(s) constituting the functional layer has an affinity for the intermediate layer and does not have an affinity for the aerogel layer.
In any aerogel layer, the intermediate layer may be a layer which is separately formed on a surface of the aerogel layer, or a layer which is formed by transmuting a part of the aerogel layer. The intermediate layer which is formed by the transmutation of the aerogel layer is substantially inseparably unified with the aerogel layer which is not transmuted, but it is not included in the xe2x80x9caerogel layerxe2x80x9d which constitutes the aerogel substrate of the present invention. However, in the case where the intermediate layer is formed by the transmutation of the surface of the aerogel layer, xe2x80x9ca surface of the aerogel layerxe2x80x9d refers to a surface of the intermediate layer so far as a particular mention is not made.
Any one of the aerogel substrates of the present invention can be said to be a functional substrate of which functional layer can perform a predetermined function. In this specification, the term xe2x80x9csubstratexe2x80x9d is used in a sense as including a plate member (including a plate, a sheet and a film) of which thickness dimension is considerably smaller than the other dimensions, and a rectangular solid and a cube which have a thickness dimension which is of generally the same order as those of the other dimensions. The substrate includes a plate, a rectangular solid and a cube in which a part of surface is curved. Therefore, each layer which constitutes the aerogel substrate may be in the form of a plate, a sheet, a film, a rectangular solid, or a cube depending on the final form of the aerogel substrate.
The embodiments of the aerogel substrates according to the present invention will be described below.
In the first aspect of the present invention, the first embodiment of the aerogel substrate is an aerogel substrate comprising a hydrophobic aerogel layer, a hydrophilic layer which is formed by subjecting at least one surface of the hydrophobic aerogel layer to a hydrophilicizing treatment (a treatment for imparting hydrophilicity), a coating layer which is formed on a surface of the hydrophilic layer, and a functional layer which is formed on the coating layer. In the first embodiment of the first aspect, the intermediate layer consists of the hydrophilic layer which is formed by subjecting the surface of the hydrophobic aerogel layer to the hydrophilicizing treatment and the coating layer which is formed on the surface of the hydrophilic layer. xe2x80x9cSubjecting a hydrophobic aerogel layer to a hydrophilicizing treatmentxe2x80x9d means removing hydrophobic groups which exist in the hydrophobic aerogel layer, and the hydrophilic layer is a layer in which the hydrophobic groups have been removed.
In this aerogel substrate, the hydrophilic layer and the coating layer are interposed as the intermediate layer between the functional layer and the aerogel layer and function as a base layer for forming the functional layer uniformly. As described below, the hydrophilic layer formed on the surface of the hydrophobic aerogel layer makes it possible for the coating layer to be formed thereon uniformly without penetration of a film-forming component(s) and water into the hydrophobic aerogel layer when the coating layer is formed by coating the surface of the hydrophilic layer with an aqueous solution and/or an aqueous dispersion of the film-forming component(s) followed by drying the solution and/or the dispersion. The coating layer fills or coats the pores in the surface of the hydrophilic layer and prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer when the functional layer is formed on the surface of the coating layer.
In the first aspect of the present invention, the second embodiment of the aerogel substrate is an aerogel substrate comprising a hydrophobic aerogel layer, a hydrophilic layer which is formed by subjecting at least one surface of the hydrophobic aerogel layer to a hydrophilicizing treatment, and a functional layer which is formed on a surface of the hydrophilic layer. In the second embodiment of the first aspect, the intermediate layer is the hydrophilic layer which is formed by subjecting the surface of the hydrophobic aerogel layer to the hydrophilicizing treatment. This aerogel substrate is a variation in which the coating layer of the above described first embodiment of the aerogel substrate of the first aspect corresponds to the functional layer, which is formed directly on the surface of the aerogel layer (i.e. the intermediate layer). In this aerogel substrate, even if an aqueous solution and/or an aqueous dispersion comprising a film-forming component which is coated on the hydrophilic layer may penetrate into the hydrophilic layer because the surface of the hydrophobic aerogel layer has been transmuted to be hydrophilic, such solution and/or dispersion cannot move from the hydrophilic layer into the hydrophobic aerogel layer. That is, in this aerogel substrate, the combination of the materials which form the aerogel layer, the intermediate layer and the functional layer prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer.
In the first aspect according to the present invention, the third embodiment of the aerogel substrate is an aerogel substrate comprising an aerogel layer, an inorganic layer or an organic layer which is formed by a gas phase method on at least one surface of the aerogel layer, and a functional layer which is formed on a surface of the inorganic layer or the organic layer. In the third embodiment of the first aspect, the intermediate layer is the inorganic layer or the organic layer which is formed by the gas phase method. The inorganic layer or the organic layer formed by the gas phase method fills or coats the pores in the surface of the aerogel layer and prevents the material(s) Which constitutes the functional layer from penetrating into the aerogel layer when the functional layer is formed on the surface of the inorganic or organic layer. Further, the inorganic or organic layer gives a smooth surface to function as a base coat for forming the functional layer uniformly.
In the first aspect according to the present invention, the fourth embodiment of the aerogel substrate is an aerogel substrate comprising an aerogel layer, a welded layer which is formed by heating at least one surface of the aerogel layer, and a functional layer which is formed on a surface of the welded layer. In the fourth embodiment of the first aspect, the intermediate layer is the welded layer which is formed by heating at least one surface of the aerogel layer. The xe2x80x9cwelded layerxe2x80x9d is a layer which has been densified by closing the pores in the aerogel layer. The material(s) which constitutes the functional layer formed on the surface of the welded layer cannot penetrate into the aerogel layer since the formation of the welded layer closes the pores in the vicinity of the surface of the aerogel layer. The welded layer generally has a smooth surface, which also contributes to uniform formation of the functional layer.
In the first aspect according to the present invention, the fifth embodiment of the aerogel substrate is an aerogel substrate comprising an aerogel layer, a Langmuir-Blodgett film which is formed on at least one surface of the aerogel layer, and a functional layer which is formed on a surface of the Langmuir-Blodgett film. In the fifth embodiment of the first aspect, the intermediate layer is the Langmuir-Blodgett film. The Langmuir-Blodgett film fills or coats the pores in the surface of the aerogel layer and prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer when the functional layer is formed on the surface of the Langmuir-Blodgett film. The Langmuir-Blodgett film generally has a smooth surface, which also contributes to uniform formation of the functional layer.
In the first aspect according to the present invention, the sixth embodiment of the aerogel substrate is an aerogel substrate comprising an aerogel layer, an inorganic layered compound layer which is formed on at least one surface of the aerogel layer, and a functional layer which is formed on a surface of the inorganic layered compound layer. In the sixth embodiment of the first aspect, the intermediate layer is a layer of the inorganic layered compound. The inorganic layered compound layer fills or coats the pores in the surface of the aerogel layer and prevents the material(s) which constitutes the functional layer from penetrating into the aerogel layer when the functional layer is formed on the surface of the inorganic layered compound layer. The inorganic layered compound layer generally has a smooth surface, which also contributes to uniform formation of the functional layer.
In any aerogel substrate of the above first to sixth embodiments of the first aspect, the aerogel layer is preferably made of a silica aerogel.
By forming the functional layer as a layer which performs a desired function, it is possible to produce an aerogel substrate of the present invention as a desired functional substrate. The functional layer is, for example, an electrically conductive thin film, an infrared ray reflective thin film, an optical waveguide thin film, a transparent and electrically conductive thin film, or a fluorescent layer.
An aerogel substrate of which functional layer is the electrically conductive thin film can be used as a circuit board by forming a circuit pattern with the electrically conductive thin film. The electrically conductive material thereof is an electrically conductive metal which is selected from copper, aluminum, magnesium, silver and the like. The electrically conductive material is preferably copper from the viewpoints of electrical conductivity and cost. The circuit pattern is formed by subjecting the electrically conductive metal thin film to treatments including the photoresist formation, the masking, the exposure, the development and the etching.
In the case where the aerogel layer of the circuit board is a silica aerogel layer, the circuit board can be used as an excellent circuit board having a low dielectric constant and is useful as a substrate for a large-scale integrated circuit. This is because the silica aerogel has a very low dielectric constant of about 1.05 to about 2.0.
An aerogel substrate having the infrared ray reflective thin film can be used as a heat insulating substrate since the substrate can reflect infrared rays. The infrared ray reflective thin film is, for example, a thin film of aluminum or titania.
In the case where the aerogel layer of the heat insulating substrate is a silica aerogel layer, a thermal conductivity of the substrate is reduced, and therefore the aerogel substrate shows more excellent heat insulating properties. This is because the silica aerogel has a very low thermal conductivity of about 0.01 to 0.025 W/mK and a very low density.
An aerogel substrate having an optical waveguide thin film can be used as an optical waveguide substrate which transmits a light in a predetermined direction. In this aerogel substrate, a light is totally reflected at the interface between the aerogel layer and the optical waveguide thin film (such as a transparent thin film made of an inorganic oxide), and therefore the optical waveguide thin film functions as an optical waveguide path with a high optical transmission performance. The optical waveguide thin film is a transparent film having a large refractive index and made of a material for an optical fiber, such as silica.
In the case where a dense layer (e.g. film) is disposed as the intermediate layer between the optical waveguide thin film and the aerogel layer as in the aerogel substrates of the first embodiment and the third to sixth embodiments in the first aspect, a thickness of the intermediate layer is preferably 300 nm or less, and more preferably 100 nm or less. If the thickness of the layer is larger than a wavelength of the light to be transmitted, the light cannot be transmitted.
In the case where the aerogel layer of the optical waveguide substrate is a silica aerogel layer, a total reflectivity at the interface between the optical waveguide path and the aerogel layer is increased, and therefore the light transmission loss is considerably reduced even if the optical waveguide path is formed into a curved pattern. This is because the silica aerogel has a very low refractive index of 1.008 to 1.3.
The aerogel substrate having the transparent and electrically conductive thin film can be used as a substrate for a light emitting device. This transparent and crystal as well as a function of a touch panel. This is because a silica aerogel has a very low refractive index and the same optical function as that of air.
An aerogel substrate having the fluorescent layer can be used as a light emitting device. The light is emitted from the fluorescent layer by irradiation of an ultraviolet ray. Similarly to the light emitting device described above, where the aerogel layer is the silica aerogel layer, an external efficiency upon coupling out the light generated in the fluorescent layer can be increased. The fluorescent layer is made of, for example, an inorganic fluorescent material such as Y2O3:Eu (red), LaPO4:Ce, Tb (green), BaMgAl10O17:Eu (blue) or the like, or an organic fluorescent material such as a low molecular weight dye material, a conjugated polymer material or the like.
Each layer described above is an example of the preferred functional layer. The functional layer may perform other function. Further, the term xe2x80x9cfunctional layerxe2x80x9d is used in the sense of including a layer which gives a desired property to the substrate comprising the aerogel layer and provides a certain effect. For example, the functional layer includes a colored thin film which is formed so as to give a decorative effect to the surface of the aerogel layer.
In the second aspect, the present invention provides a electrically conductive thin film can be made of a transparent and electrically conductive material selected from indium-tin oxide (ITO), indium-zinc oxide (IXO), silver, chromium and so on. The aerogel substrate having the transparent and electrically conductive thin film can constitute, for example, an EL light emitting device. The EL light emitting device is formed by providing an EL (electroluminescence) layer on a surface of the transparent and electrically conductive thin film of the aerogel substrate and providing a back metal electrode on a surface of the EL layer. The EL layer can be made of a luminescent material conventionally used in the organic EL or inorganic EL. The light is emitted from the EL layer by applying an electric field between the transparent and electrically conductive thin film and the back metal electrode. This EL light emitting device can be used for various kinds of displays.
The light emitting device in which the aerogel layer is a silica aerogel layer can be used as an EL light emitting device of which external efficiency upon coupling out the light generated in the EL layer is high. This is because the silica aerogel has a very low refractive index of 1.008 to 1.3. Further, the light emitting device comprising the silica aerogel layer make it possible to produce a display having a function of protection of a front light for a reflective liquid process for producing the aerogel substrate in the first aspect according to the present invention.
The process for producing the aerogel substrate of the present invention comprises the steps of:
forming an intermediate layer on at least one surface of an aerogel layer; and
forming a functional layer on a surface of the intermediate layer,
said intermediate layer being a layer which prevents a material(s) which constitutes the functional layer from penetrating into the aerogel layer.
The aerogel substrates of the first embodiment and the third to the sixth embodiments provided by the present invention in the first aspect, can be produced by forming the intermediate layer according to the following methods.
The process for producing the aerogel substrate of the first embodiment in the first aspect comprises the steps of:
forming a hydrophilic layer by subjecting at least one surface of a hydrophobic aerogel layer to a plasma treatment or a UV ozone treatment;
forming a coating layer by coating a surface of the hydrophilic layer with an aqueous solution and/or an aqueous dispersion of a film-forming component(s) followed by drying the solution and/or the dispersion; and
forming a functional layer on a surface of the coating layer.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the hydrophilic layer by subjecting at least one surface of the hydrophobic aerogel layer to the plasma treatment or the UV ozone treatment; and forming the coating layer by coating the surface of the hydrophilic layer with the aqueous solution and/or the aqueous dispersion of the film-forming component(s) followed by drying the solution and/or the dispersion.
According to this production process, a surface which is suitable for forming the functional layer uniformly thereon is provided by forming the coating layer on the surface of the hydrophobic aerogel layer, and the hydrophilicizing treatment of the hydrophobic aerogel layer makes it possible to form the coating layer on the surface thereof.
The coating layer is formed by coating the surface of the hydrophilic layer with the aqueous film-forming component(s) solution and/or the aqueous film-forming component(s) dispersion followed by drying the solution and/or the dispersion. xe2x80x9cFilm-forming componentxe2x80x9d is a component which constitutes a film after a solution or a dispersion containing the component is coated and thereafter dried to remove a solvent. As xe2x80x9cthe aqueous solution and/or the aqueous dispersion of the film-forming component(s)xe2x80x9d,are listed a) an aqueous solution of the film-forming component(s), b) an aqueous dispersion of the film-forming component(s), and c) a fluid containing at least two film-forming components, at least one component being dissolved in water and at least one other component being dispersed in water.
The aerogel represented by the silica aerogel is porous. When a liquid substance is applied onto the aerogel, the liquid substance easily penetrates into the aerogel due to the capillarity, whereby the microporous structure of the aerogel may be broken resulting deterioration of the properties of the aerogel. For the aerogel which has not been to subjected to the hydrophobing treatment, its microporous structure is broken when either of a water-based liquid substance or an oil-based liquid substance penetrates therein. It is substantially impossible to form a film on such aerogel by applying a liquid for coating.
On the other hand, for the hydrophobic aerogel, i.e. an aerogel to which hydrophobicity has been imparted, the microporous structure is not broken by the penetration of the water-based liquid, although the microporous structure is broken by the penetration of the oil-based liquid substance. Therefore, no break of the microporous structure is caused even if a film is formed on the surface of the hydrophobic aerogel using the water-based liquid for coating (i.e. an aqueous solution and/or an aqueous dispersion of the film-forming component(s)) according to the conventional coating method (for example, the spin coating method). However, it is actually difficult to apply the water-based liquid for coating uniformly on the surface of the hydrophobic aerogel since hydrophobic organic groups which repel the aqueous solution and/or the aqueous dispersion are bound to the surface of the hydrophobic aerogel.
In the process for producing the aerogel substrate of the first embodiment in the first aspect, the organic hydrophobic groups on the surface of the aerogel are removed by subjecting the surface of the hydrophobic aerogel layer to the plasma treatment or the UV ozone treatment while its hydrophobicity is maintained in the inside. By the removal of the hydrophobic groups, a hydrophilic layer is formed in the surface of the aerogel layer, and thereby the aqueous solution and/or the aqueous dispersion of the film-forming component(s) as the liquid for coating can be applied uniformly onto the surface of the aerogel layer and a film-like coating layer is formed after drying to remove water. The coating layer fills or coats the pores in the surface of the aerogel layer and preferably has a smooth surface. There is no case where the aqueous solution and/or the aqueous dispersion penetrates inside to break the microporous structure since the inside of the aerogel layer remains hydrophobic.
The plasma treatment can be carried out by a known method conventionally used for carrying out surface cleaning or the like.
The UV ozone treatment also can be carried out by a known method. Concretely, the treatment is carried out by a method in which the oxygen in the air is ozonized by irradiation of ultraviolet rays to produce oxygen radicals and the aerogel surface is etched and cleaned with the radicals.
The plasma treatment or the UV ozone treatment is preferably carried out such that the thickness of the hydrophilic layer in which the hydrophobic groups in the aerogel have been removed is in the range of 50 nm to 100 xcexcm.
The process for producing the aerogel substrate of the third embodiment in the first aspect comprises the steps of:
forming an inorganic layer or an organic layer by a gas phase method on at least one surface of an aerogel layer; and
forming a functional layer on a surface of the inorganic layer or the organic layer.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the inorganic layer or the organic layer by the gas phase method on at least one surface of the aerogel layer.
The gas phase method (or a vapor growth method) is a method for forming a film by evaporating a film-forming material(s) in vacuum or forming a plasma material(s) in vacuum followed by depositing such material(s) on a surface of an object (i.e. the aerogel layer in the present invention) to form a film. Concretely, a CVD (Chemical Vapor Deposition) method, a sputtering method, or a vapor deposition (vacuum deposition) can be employed as the gas phase method.
The inorganic layer or the organic layer which coats or fills the pores in the surface of the aerogel layer is formed by the gas phase method. The smoothness of the surface of the inorganic layer or the organic layer can be improved by appropriately selecting conditions of the gas phase method. The formation of the inorganic layer or the organic layer by means of the gas phase method does not cause the break of the microporous structure of the aerogel since the gas phase method is a dry process which does not involve coating a liquid substance followed by drying the substance. Therefore, this production process can be applied to both of the hydrophobic aerogel or the aerogel which has not been subjected to the hydrophobing treatment.
The thickness of the inorganic layer or the organic layer formed by the gas phase method is preferably 50 nm to 100 xcexcm.
The process for producing the aerogel substrate of the fourth embodiment in the first aspect comprises the steps of:
forming a welded layer by heating at least one surface of an aerogel layer; and
forming a functional layer on a surface of the welded layer.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the welded layer by heating at least one surface of the aerogel layer.
An annealing treatment in which at least one surface of the aerogel layer is heated results in closing the pores in the vicinity of the surface of the aerogel layer, and thereby a dense intermediate layer which is not porous is formed. Heating the aerogel layer is carried out by placing the aerogel layer in a high temperature furnace for several tens of seconds, or by irradiation of heat rays onto the surface for short period of time. In any method, heating is preferably carried out such that the thickness of the welded layer is in the range of 50 nm to 100 xcexcm. This production process can be applied to both of a hydrophobic aerogel or an aerogel which has not been subjected to the hydrophobing treatment since this method does not involve coating a solution and so on upon making the surface of the aerogel layer smooth.
The process for producing the aerogel substrate of the fifth embodiment in the first aspect comprises the steps of:
forming a thin film on at least one surface of an aerogel layer by the Langmuir-Blodgett method; and
forming a functional layer on a surface of the thin film.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the thin film on at least one surface of the aerogel layer by the Langmuir-Blodgett method.
In this production process, the thin film as the intermediate layer is formed on a surface of the porous aerogel layer by the Langmuir-Blodgett method, which film coats or fills the pores in the surface of the aerogel layer. The Langmuir-Blodgett method (which is referred to also as xe2x80x9cLB methodxe2x80x9d)is a method for forming a thin film in which method a polymer membrane is formed on a water surface by spreading a polymer solution which is insoluble into water; the surface of the aerogel layer is contacted with the polymer membrane at an appropriate surface pressure; and thereby the polymer membrane is transferred from the water surface to the surface of the aerogel.
The thickness of the thin film formed by the LB method is within a monomolecular level, and therefore, the LB method makes it possible to form a very thin film having a thickness of several nanometers or others within the same order. Further, the film thickness can be controlled by the nanoscale by varying a length of a side-chain of the polymer. Furthermore, as described below, by a built-up technique for building up a polymer thin film on the surface of the aerogel layer such as a vertical dipping method or a horizontal dipping method, a built-up film structure and properties of the film surface can be changed. Upon forming the polymer thin film by the LB method, as the polymer, a polymer having an amphipatic property which is selected from a polyimide, a polyalkylacrylate, a polyester, a polyvinylacetal, a polyglutamate and so on can be used.
The process for producing the aerogel substrate of the sixth embodiment in the first aspect comprises the steps of:
forming an inorganic layered compound layer by having at least one surface of an aerogel layer adsorb an inorganic layered compound; and
forming a functional layer on a surface of the inorganic layered compound layer.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the inorganic layered compound layer by having at least one surface of the aerogel layer adsorb the inorganic layered compound.
In this production process, the surface of the aerogel layer on which the functional layer is formed is coated with the inorganic layered compound layer. The inorganic layered compound layer coats or fills the pores in the surface of the aerogel layer to prevent the material(s) which constitutes the functional layer formed on its surface from penetrating into the aerogel layer. Generally, the inorganic layered compound layer provides a smooth surface to ensure that the functional layer is formed more uniformly. The inorganic layered compound layer is formed by contacting the surface of the porous body with a treatment liquid which includes the inorganic layered compound dispersed in a solvent, and thereby having the surface of the aerogel layer adsorb the inorganic layered compound. xe2x80x9cAdsorbxe2x80x9d means forming the inorganic layered compound layer without involving the solvent of the treatment liquid in which the inorganic layered compound is dispersed in the formation of the inorganic layered compound layer in the course of the formation of the layer on the surface of the object (i.e. the aerogel layer in the present invention). This production process can be applied to both of a hydrophobic aerogel and an aerogel which has not been subjected to the hydrophobing treatment since this process does not require the application of a liquid substance on the surface of the aerogel layer.
In any one of the production processes described above, the functional layer is formed by a coating method or a gas phase method.
The coating method is a method for forming a film by coating a surface of an object with a liquid in which a film-forming component(s) is dissolved and/or dispersed in a solvent followed by drying the liquid to remove the solvent. The coating method is a conventional film forming method. Concretely, the spin coating method, the dip coating method, the spray coating method, the bar coating method and the like are known.
The gas phase method is the same as described with respect to the production process of the aerogel substrate of the third embodiment in the first aspect. The gas phase method makes it possible to control the thickness of the layer to be formed to a very thin thickness (for example, several hundreds of nanometers). Such control cannot be achieved by the coating method.
In the third aspect, the present invention provides a process for producing the aerogel substrate of the second embodiment in the first aspect.
The process for producing the aerogel substrate of the second embodiment in the first aspect comprises the steps of:
forming a hydrophilic layer by subjecting at least one surface of a hydrophobic aerogel layer to a plasma treatment or a UV ozone treatment; and
forming a functional layer by coating a surface of the hydrophilic layer with an aqueous solution and/or an aqueous dispersion of a film-forming component(s) followed by drying the solution and/or the dispersion.
This production process is characterized in that the step of forming the intermediate layer comprises the step of forming the hydrophilic layer by subjecting at least one surface of the hydrophobic aerogel layer to the plasma treatment or the UV ozone treatment.
This production process is a variation of the production process of the aerogel substrate of the first embodiment in the first aspect wherein the functional layer is formed directly on the surface of the hydrophilic layer without forming the coating layer. This production process can be applied when the functional layer is formed by applying the aqueous solution and/or the aqueous dispersion of the film-forming component(s) followed by drying the solution and/or the dispersion. The aqueous solution and/or the aqueous dispersion which is used in forming the functional layer contains a component(s) as the film-forming component(s) which gives a desired function to the substrate. For example, a transparent and electrically conductive thin film can be formed as the functional layer by coating the surface of the hydrophilic layer with an aqueous solution and/or an aqueous dispersion containing indium-tin oxide as the film-forming component followed by drying the solution and/or the dispersion.